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The current trend is towards fluid designs that will make use of all the available screen width, regardless of user resolution. There are many topics on this in the CSS Forum [webmasterworld.com].
However, to answer your question, many people use a width of 750px and a height of 420px to ensure that no scrolling occurs. This should accommodate most toolbars.
HTH
There are many who use percentage sizes, i.e. 100% or perhaps less to allow borders instead of fixed sizes, so as to allow the table to adjust to any size. One must of course take into account any 'fixed size' table content, such as images, which will themselves push out the size of your tables.
ie:796x434
nn:792x435
as minimum values for display(640x480 no use)
it is need to detect what size of your screen depend of your browser. After it divide browser screen into some table cells. For more resolution than 800x600 just create background-images to some parts of table cells.
Don't worry about 640x480 users.. your site will still load and they'll be used to scrolling about to read things. 800x600 users might account for up to 50% of your traffic though.